1. Field of the Invention
This invention relates to a process for the preparation of oxalyl dihydrazide and the use of oxalyl dihydrazide in gas generating compositions. More particularly, this invention concerns the addition of oxalyl dihydrazide to perchlorate-based gas generating compositions to improve their combustion characteristics so that they can be used for such applications as gas turbine and jet engine starters and with proper safety precautions in automobile protective crash bag inflation.
The novel coolant of this invention has the structure ##EQU1## The process for preparation of the above oxalyl dihydrazide material is described below.
2. Description of the Prior Art
Within recent years, especially where applications in the aerospace or aeronautical fields are concerned, there has been an increasing reliance upon the use of devices driven or actuated through the generation of gases. These devices commonly derive their energy from the controlled combustion of solid gas-generating compositions in the gas turbine engines. The combustion of these solid compositions to gaseous products can be used to pressurize a fluid or drive a turbine to produce mechanical or electrical energy or to start various mechanical devices. The gas-generating devices are particularly advantageous in that they are capable of producing a rather substantial amount of power considering the relatively light weight of the fueled gas generator compared to conventional gas or oil powered generators. Because of their high power to low weight ratio, these devices are especially suited to drive gas turbines and jet type engines for intermittant or short term use.
Recently a novel group of coolants has permitted the use of perchlorate oxidizers in gas-generating compositions. These compositions are disclosed in U.S. Pat. Nos. 3,193,421 and 3,214,304. Specifically the above disclosures teach that when energetic perchlorates heretofore unusable as oxidizers in gas-generating compositions are formulated with oxalohydroxamic acid, also referred to as dihydroxyglyoxime (DHG) and related compounds, a substantial decrease in flame temperature is obtained. More recently, dihydroxglyoxime (DHG) and related compounds have been used as coolants in gas-generating compositions containing polynitrated organic or polynitro organic oxidizers replacing the perchlorate oxidizer. These compositions are disclosed in U.S. Pat. No. 3,362,859. It is therein taught that for certain applications where corrosion or erosion problems are critical that perchlorate oxidizers are unsuitable because of the corrosive effects of the hydrogen chloride gas produced during combustion. As a general teaching, this is accurate. However, perchlorate-based gas-generating compositions remain quite useful in applications where corrosion or erosion is not a critical problem. Thus, for example, in many military gas turbine starter applications, the hardware downstream from the starter exhaust is constructed of metal which is highly resistant to corrosion or errosion. In addition, any hydrogen chloride gas produced during combustion of the perchlorate-based gas-generating composition does not normally remain in the gas turbine for a significant period of time since such gas is purged from the system by non-corrosive gases generated by the fuel used to operate the gas turbine.
The perchlorate-based gas-generating compositions of the present invention are useful to a limited degree in applications such as inflatable gas bags because of their relatively low flame temperatures. In this latter application, care is required to design an inflatable bag which is impermeable to hydrogen chloride gas and which is unlikely to rupture during inflation.
Gas-generating compositions useful in the applications to which this invention is directed must meet a number of requirements which are difficult to satisfy. Thus, gas-generating compositions must be ballistically stable after prolonged storage at extreme temperatures ranging from as high as 180.degree.F to as low as -80.degree.F. In addition, particularly for aerospace and military applications, the compositions must be readily ignitable within these same temperature ranges. Furthermore, the compositions must be relatively insensitive to shock, be heterogeneous in content, have substantial elasticity to minimize gaps or voids and burn evenly and consistently. Finally, the oxidizer in gas-generating compositions must have a relatively slow burning rate and burn at relatively low flame temperatures.
The most difficult of these requirements has been the attainment of relatively low flame temperatures. In this context the term relatively low flame temperature is more readily understood by comparison between the flame temperatures of gas-generating compositions and solid rocket propellant compositions. For example, it is well known in the propellant art that propellant compositions have flame temperatures on combustion in the neighborhood of 4000.degree.F to 5000.degree.F or more. Such high flame temperatures are destructive to parts fabricated of commercial metal alloys such as the stainless steels over any sustained period of time. In fact, prolonged exposure to these higher temperatures attack many of the specially formulated so called "heat resistant alloys". However, the erosion and corrosion of the metal missile parts due to the high flame temperatures produced in combustion is of little importance in missiles since they are designed as expendable "one-shot" pieces of hardware. On the other hand, gas-generating compositions used in such applications as starters for gas turbines or jet engines must operate at much lower flame temperatures in order to avoid damage to the gas turbine or jet engine. In these applications, there is a continuing demand for gas-generating compositions with lower flame temperatures. For example, in certain military gas turbine applications, the gas-generating composition must operate at flame temperatures of less than about 2000.degree.F. In other military and commercial gas turbine applications it is anticipated that flame temperature requirements will arise for compositions having flame temperatures of less than 1500.degree.F or perhaps even lower. In comparison with the flame temperatures of propellant compositions (i.e. 4000.degree.F or higher) these are relatively low flame temperatures.
It is evident from the requirements existant in the field of gas-generating compositions that a need exists for gas-generating compositions with flame temperatures lower than those yet achieved in the compositions of the prior art.
Accordingly, it is an object of this invention to prepare novel gas-generating compositions superior in several aspects to compositions of the prior art. It is a further object of this invention to prepare gas-generating compositions which are stable, easily ignitable, and whose combustion is smooth and continuous. It is a still further object of this invention to prepare solid gas-generating compositions which upon combustion produce lower flame temperatures than has been possible with other gas-generating compositions of the prior art. Finally, it is an object of this invention to provide a process for the manufacture of oxalyl dihydrazide.
Other objects will become apparent to those skilled in the art from a consideration of the following detailed description.